Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $160.53   5.447%   $169.2741   $169.27   $169.25   $169.30  
  Purchase #2 $44.30   9.644%   $48.5723   $48.57   $48.55   $48.60  
  Purchase #3 $25.91   13.745%   $29.4713   $29.47   $29.45   $29.50  
  Purchase #4 $248.51   5.762%   $262.8291   $262.83   $262.85   $262.80  
  Purchase #5 $128.26   10.562%   $141.8068   $141.81   $141.80   $141.80  
  Purchase #6 $59.30   13.457%   $67.28   $67.28   $67.30   $67.30  
  Purchase #7 $228.70   7.243%   $245.2647   $245.26   $245.25   $245.30  
  7 purchase totals = $895.51       $964.4983   $964.49   $964.45   $964.60